1. Field of the Invention
The present invention relates to an improved method and associated apparatus for employing powdered activated carbon in withdrawing mercury from exhaust gases in coal fired power plants with subsequent desorption permitting reuse of the powdered activated carbon in the separation process or, if desired when spent, as a contribution to fuel. More specifically, the present invention relates to an initial filtering stage removing coarse particles followed by introduction of powdered activated carbon which is separated from the exhaust gas in a fine particle filter to permit subsequent elevated temperature desorption to separate the mercury and inert gas from the powdered activated carbon.
2. Description of the Prior Art
It has been known to employ various means to separate both particulate and gaseous components of coal fired power plants before discharge of the exhaust gas to the atmosphere. For example, it has been known to employ electrostatic precipitators as well as bag houses and other forms of filtration.
It has been known to purify a carbon-containing adsorption medium for treating a flue gas with subsequent regeneration and reusing or burning of the absorption medium which is said to be in the form of pellets, lumps or granules. See U.S. Pat. No. 5,409,812.
It has been known to add a carbon-containing absorbent to a gas stream with an objective being recovery of mercury. See, generally, U.S. Pat. Nos. 4,889,698; 5,409,812; 5,505,766; 5,672,323; 5,827,352; 6,027,551; 6,558,642; 6,582,497; and 6,589,318; as well as published United States patent applications 20020033097 and 20020124725.
It has also been known to inject activated carbon into a flue gas treatment system having an electrostatic precipitator and a wet flue gas desulphurization tower to remove mercury. See U.S. Pat. No. 5,672,323.
It has also been known to remove fly ash through a coarse particle filter as well as the use of fine particle removal devices. See, generally, U.S. Pat. Nos. 4,889,698; 5,409,522; 5,409,812; 5,672,323; 5,827,352; and 6,027,551.
U.S. Pat. No. 6,589,318 discloses catching the sorbent in a fine particle separator.
Desorption of mercury from a sorbent in various environments employing carbon base sorbents, as well as other approaches, has been known. See, generally, U.S. Pat. Nos. 6,346,936; 6,103,205; 6,097,011. It has also been known to effect desorption in an inert or oxygen-free atmosphere. See, generally, U.S. Pat. Nos. 6,346,936; 6,097,011; and 6,027,551.
U.S. Pat. No. 5,409,812 discloses desorbing mercury from mercury-bearing powdered activated carbon using an undisclosed desorption gas and reusing the treated powder activated carbon.
In spite of the foregoing disclosures, there remains a very real and substantial need to provide an improved method and associated apparatus for removing mercury from coal fired power plant exhaust gas in an efficient unburdensome and safe manner.